Artificially-cooled high-frequency coil



E. F. NORTHRUP.

ARTIFICIALLY COOLED HIGH FREQUENCY COIL. APPLICATION FILED APR. 18, 1919.

1,328,336, Patented Jan. 20, 1920.

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Eel-N1; F Norillrup UNITED STATES PATENT oFFIoE.

EDWIN F. NORTHRUP/OF PRINCETON, NEW JERSEY, ASSIGNOR TO THE AJAX METAL COMPANY, OF PHILADELPHIA. PENNSYLVANIA. A CORPORATION OF PENNSYL- VANIA.

ARTIFIGIALLY-COOLED HIGH-FREQUENCY COIL.

Patented Jan. 20, 1920.

Application filed April 18 1919. Serial No. 291,161.

To all whom it may concern: I

Be it known that I, EDWIN F. NoRTHRpr, a citizen of the United States, residing at 30 Wiggins street, Princeton, in the county of Mercer and State of New Jersey, have invented a certain new and useful Artificially-Cooled High-Frequency 'Coil, of which the following isa specification.

My invention relates to high frequency induction heating apparatus well illustrated by electric furnaces.

The purpose of my invention is to artificially cool an induction coil carrying high frequency current 1n order to malntam tie coil at a low temperature and correspondingly low resistance, to increase the currentcarrying capacity and improve the msulation.

A further purpose is to produce the materials described and simllar materials and to use the methods 'by which they are prop duced.

My Patents, Nos. 1,286,394 and 1,286,395 both of December 3, 1918, as well as several pending applications, are directed to the utilization of high frequency electric current in the inductive transfer of heat, presenting various arrangements and constructions among the many by which this result may be attained.

By artificially cooling the inductor coil, I have found that there is practically no limit to the temperature which can be attained, without necessity for interlinkage of transformer iron and with any special conditions desired,including carbon free treatment and melting, and application of a vacuum. The artifical cooling is of benefit in improving the efliciency of high frequency inductive heating even where high temperatures are not required.

The turns of the coil may safely be wrapped much closer together and the coil itself may be placed closer to the resistor heated, without increase of coilresistance by reason of temperature rise and without danger of short-circuiting between the turns of the coil or between the coil and the other apparatus by reason of ionization of the air about the coil.

The artificial cooling of the coil makes possible also the use of other insulations or dielectrics, without consequent over-heating from the closing of this space about the coil. The insulation can be chosen without regard to its capacity to stand heat as it can be maintained at room temperature if desired.

Recognizing that this invention is applicable to any kind, form or shape of hlgh.

frequency coil, to which the high frequency current is applied by any means whatever, and with any form of artificial cooling, 1 have selected for illustration the simplest form 'of current supply, paralleling Figure 1 of each of my two patents above indicated, have applied the high frequency current to an extremely simple form of inductor furnarie and have utilized water-cooling of the col Fig. 1 is a diagrammatic view showing a silmple form of lngh frequency current sup- P Fig. 2 is a vertical central section of a form of furnace to which my invention is applied.

Fig. 3 is a broken section of a modified form;

Similar numerals indicate like parts in the drawings.

The single phase alternating current line terminals A, N are shown as charging a ca pacity C through a heating coil 0. The gap provides for discharge of the capacity 0 through the coil. The inductance and resistance of the coil circuit are indicated diagramn'iatically by L L B R, and the inductances of the exterior circuit are indicated as L L. Any suitable artificially cooled coil is shown at O and a crucible or other container or resistor to be heated is inclosed by the coil.

In Fig. 2, complying with the statute, I

have indicated one means of carrying out my invention, but without any intention of restricting to this means and in fact with knowledge that the artificial cooling may be applied to any form of high frequency coil, cxternal to either a solid or hollow conductor or within a hollow conductor and by any system of artificial cooling suitable to the type or shape of coil or the c'lmracter, section, material, location or use of coil conductor to which it is to be applied.

lVith this explanation, I will proceed to describe the form shown in Fig. 2

The base 1 is apertured at 2 for convenient withdrawal of the parts and the aperture is normally closed by a slide ,3. Upon this base I rest a cylinder 4, within which is insulating material is sifted in about the supply.

cylinder.

In Fig. 1 the cylinder 7 is shown as having a closed bottom at 7 as may be desired if it be a crucible intended to pour from the top. Either the cylinder or a crucible, so used, may be electricallyconductmg, where it is to form the resistor to heat an electrically conducting or non conducting content, or electrically non-conducting where the current is to be induced in an electrically conducting .(resistor) content.

A cap 7 may be used if desired but has not proved necessary in the attainment of temperatures suificient to meltv highly refractory metallic oxids and metals.

The conductor forming the coil 0 is hollow, but, whether solid or hollow may be of any section. It is here shown as extending from 9, where the refrigerant enters, to 10, where it discharges, and of elliptical section, edgewise-wound as shown at 11. Where the conductor is hollow it may be supplied with anycooling content 12, such as air, oil, Water, salt solution, carbon dioxid; ammonia, etc., from any source of fluid or vapor supply desired. A liquid refrigerant possesses many advantages.

Where an electrically non-conducting in-' ternal cooling medium is used the conductor may be insulated at both ends by a non-conductin length, such as rubber, effectively insulating the applied electrical current f a conducting liquid be used as the sup- P y different way, at one or at both ends, as by insulating the source of liquid supply and discharging the liquid in the form of a spray as at 10, with suflicient drop to break the conducting continuity of the spray. As a precaution I have shown the spray in Fig. 2, though the resistance of the water there used would probably form sufficient insulation.

The high frequency electric current, whether from a special generator or obtained by oscillatory discharge of condensers, is applied to the coil at 13,14 or 13', 14' from a source of high frequency supply 15, 16 or 15', 16, which may be directly generated or represent the oscillatory discharge from condensers and, correspondingly, may vary widely in voltage. For a resistor of circular section the helical form of coil shown is desirable. This may be greatly varied.

is then put in a it is desirable to break the circuit in av Where the cooling medium is to be applied to the exterior of the high frequency coil, it is undesirable to use a conductor of hollow section because it reduces the number of turns per unit length. In Fig. 3 a coil of fiat conductor 11', edgewise wound, is shown with an exterior-1y applied cooling medium in the space 17 between walls 18, 18. It may have either inlet or discharge at 19, the other not being shown, with forced or natural thermal circulation as preferred.

All of the other parts shown are preferably of highly refractory material whose form and composition Wlll be dictated by convenience of the necessities of the intended use. Excellent results have been obtained using quartz for the outer cylindertreating, especially with the ferrous metals.

For the higher temperatures such as are required for melting platinum I substitute zirconia sand for the silex sand used with lower temperatures and with a temperature elevation obtained limited by no other consideration than the heat resistance of the materials holding the melt.

In operation, with the form shown, the slide is placed in position, sand is sifted within the outer cylinder to the desired height before the inner refractory cylinder is placed in position and then about the inner cylinder to approximately its upper level. The material to be melted or heattreated is then inserted, the cooling medium applied and the high frequency electric current connected. ,The pressure or character of the cooling medium may beincreased or changed for the higher temperatures.

With normal water pressures and a comparatively small coil section, temperatures over 2500 C. have been attained in a cylindrical resistor mass not more than one and one half inches less in diameter than the exterior of the inducing coil, whose temperature was lower than that of the room. The prospect of exceeding the temperature of the electric are by my present invention is quite promising.

I have also melted ferrous metals and their alloys free from carbon or other elements which might even slightly affect their purity, and could melt them directly in the sand without using any container where the clay, magnesia, zirconia or other cylinder 7 is shown. The material to be melted defines a pocket or form in the sand which is occupied by the melt. The sand forms a heat insulator and mold and, at sufiic'iently high temperatures, with the particular sand chosen, melts close to the material melted, and separately or in chemical union with the material melted subsequently chills about it forming an inclosing shell. This mold-forming property of the sandrcauses it to heal any breaks in the cylinder or crucible where one is used, Without interruption to the process.

By the method of heating described, inducing current directly within an electrically conducting material (resistor) with artificial cooling of the inductor coil in a crucible free from carbon, where desired, I have not onlysucceeded in melting many metals and metallic oxids requiring high temperatures and without reduction of the oxids but have been able to control the conditions under which the melting took place.

Among the metals melted have been elec trolytic iron, electrolytic nickel, aluminum,

, molybdenum and platinum.

Alloys of pure metals requiring high temperatures have been made by me alloying such metals as iron and copper, iron and molybdenum and molybdenum and copper in different proportions.

Among the oxids which I have melted are oxids of chromium, iron, cobalt and nickel. I prefer to use a crucible for this.

I have also used the furnace for coating purposes as, for example, in the coating of the Walls of a graphite container with a carbid by covering the walls with a coating of oxidsuch as the oxid of aluminum and melting it in place to form the carbid as a coherent, continuous protective coating.

Having thus described my invention, What I claim as new and desire to secure by Letters Patent is 1. An artificially-cooled inductor furnace coil for electric inductive heating purposes, in combination With a source of high frequency current.

2. An artificially-cooledinductor furnace coil for electric inductive ,heating purposes, free from interlinkage with transformer iron.

3. An artificially-cooled inductor furnace coil for electric inductive heating purposes free from interlinkage with transformer iron, in combination with a source of high frequency current suppl 4. A hollow inductor mace coil for electric inductive heating fpurposes free from interlinkage with trans o bination with a source of high frequency rmer iron, in comelectric current supply and a cooling medium applied to the interior of the hollow.

cal form adapted to surround thdmaterial to be heated, a cooling medium applied to the coil, and high frequency current passed through the coil.

'9. A furnace comprising a coil, a support for. the coil, a refractory container for the melt and a finely divided refractorymaterial about the container, adapted to heal breaks therein, in combination with high frequency current supply therefor.

10. A high frequency inductive electric furnace utilizing a finely divided loose refractory to hold the melt.

11. A high frequency inductive electric furnace having a refractory shell limiting the melt laterally and a loose refractory bottom for the shell.

12. The process of carbon-free heatin of materials, which consists in placing t em within a carbon-free refractory and developlng the heat directly within them by electric induction while they are so placed.

13. The process of heating materials which consists in utilizing the material to be heated, to. define the mold for the melt within a finely divided refractory and inducmg a current in the material as there placed.

If. The process of melting materials requlring a high temperature, which consists in inclosing the materials within a conductor in lnductive relation thereto, artificially cooling the conductor to reduce its resistance, improve its insulation and permit closer coupling, and passing a high frequency electric current through the conductor. v

EDWIN F. NORTHRUP. 

